Encoding with C# and Java

Question

I have got to make the same function in Java and C#, but the result are not the same.

My code in C# :

    string xmlString = System.IO.File.ReadAllText(@"crc.xml");

    byte[] bytes = Encoding.ASCII.GetBytes(xmlString);

    // step 1, calculate MD5 hash from input
    MD5 md5 = System.Security.Cryptography.MD5.Create();
           
    byte[] hash = md5.ComputeHash(bytes);

    // step 2, convert byte array to hex string
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < hash.Length; i++)
    {
         sb.Append(hash[i].ToString("X2"));
    }
    Console.WriteLine(sb.ToString());

And my code in Java :

    string xmlstring = Files.readString(Paths.get("crc.xml"));
    MessageDigest m = MessageDigest.getInstance("MD5");
    byte[] digest = m.digest(xmlstring.getbytes());
    String hash = new BigInteger(1, digest).toString(16);
    System.out.println(hash);

In C# I have this result :

F5F8B2F361FEA6EA30F24BEBAA5BDE3A

But in Java I have this result :

8fb40aad49fbf796b82a2faa11cda764

What I'm doing wrong?

I think the C# byte is unsigned and the java byte is signed, that can cause the difference — SnowmanXL
– SnowmanXL, Commented Oct 12, 2020 at 14:13
If you want to calculate the MD5 of a file, you should never read the file content into a String, because that already includes a level of interpretation (namely decoding the charset) that is not necessary and can be actively harmful to the attempt. Just read the byte[] directly (or even better, stream the byte[] data, because there's no reason to have it all in memory at once). In Java the direct replacement would be Files.readAllBytes(). It seems .NET has a ReadAllBytes as well. — Joachim Sauer
– Joachim Sauer, Commented Oct 12, 2020 at 14:16
(the only reason I didn't post this as an answer is that I'm not sure that this is the specific reason for the difference here, but it is definitely an issue here). — Joachim Sauer
– Joachim Sauer, Commented Oct 12, 2020 at 14:23

Sébastian · Accepted Answer · 2020-11-04 11:38:48Z

1

Codebrane say it. Use

byte[] bytes = Encoding.UFT8.GetBytes(xmlString);

instead of

byte[] bytes = Encoding.ASCII.GetBytes(xmlString);

answered Nov 4, 2020 at 11:38

Sébastian

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